The present invention relates to power control circuits, and more particularly to a power control circuit that is suitable for protecting an electric circuit from excessive current.
Generally a current limiting fuse is used to protect an electrical circuit and its associated system when an excessive current flows through the circuit due to, for example, a short circuit accident. The current limiting fuse prevents the circuit and its associated system from being damaged, since it cuts off the excessive current when it exceeds a rated current for the circuit and associated system. A typical circuit for testing the operational short-circuit limit characteristics of a device under test (DUT) is shown in FIG. 1. The device under test may be a semiconductor device operating with a large current, such as an insulated gate bipolar transistor (IGBT), a power metal oxide semiconductor field effect transistor (MOSFET) or the like. A signal source Ss provides a signal voltage to bias the device under test. A voltage meter Vm is coupled to measure the voltage across the device under test, and a current meter Im is coupled to measure the current through the device under test. A power source Vs provides a large voltage necessary for the excessive current test of the device under test. Since the large current may be provided in a short time interval, it may be generated by charging and discharging a capacitor, as is well known in the art. A protection circuit F that includes the current limiting fuse is coupled in series between the power source and the device under test to prevent an excessive current from flowing through the test circuit when the device under test breaks down. When the device under test breaks down, there is a large possibility that the current meter and the voltage source will be damaged due to the excessive current.
The semiconductor device, such as the IGBT, may operate with high speed and with a large current. A rapid fuse is used as part of the protection circuit for cutting off excessive current at high speed. However the rapid fuse is expensive and has to be exchanged after every execution of the short circuit test of the device under test. An especially large and expensive fuse is needed for large current high speed applications. Additionally the fuse has a finite amount of inductance which becomes a source of noise when a high frequency signal is applied to it.
What is desired is a high speed, large current power control circuit that is reusable, fast in response and relatively inexpensive for protecting electronic circuits and their associated systems.